In many industrial, military, security or medical applications, images of the internal structure of objects is required. Radiography is often used for imaging. Radiography generally comprises either conventional transmission radiography or backscatter radiography.
When access behind an object to be interrogated is not possible, only backscatter radiography is possible. One method of backscatter imaging is Compton Backscatter Imaging (CBI), which is based on Compton Scattering. Compton Scattering is a phenomenon of elastic scattering of photons by electrons.
Conventional CBI is based on the utilization of single-scatter detected x-rays to form images of the first-scatter spatial distribution and thereby the object internal structure. Higher-order scatter components, which encounter more than one scattering event before emerging from the object being interrogated, are considered to be noise and conventional CBI systems are designed to minimize response to such components. Conventional CBI scanning systems can generally be divided into two classes, which both employ x-ray illumination and utilize a highly-delineated beam:                Class 1. Highly-collimated detectors with field-of-view intersecting the illumination beam at a single object internal “voxel”.        Class 2. Uncollimated, large area detectors.        
Class 1 devices are extremely inefficient in sensing the scatter field and thus yield extremely slow image acquisition. Such devices can also be insensitive to certain internal detail. Class 2 devices have fast image acquisition, but the unwanted detection of all orders-of-scattering often totally obscures the internal structural detail which is generally desired in the acquired image.
A relatively new type of imaging system based on x-ray Compton backscatter is neither a Class 1 nor a Class 2 system. Lateral migration radiography (LMR) concepts and related systems, were first disclosed in a paper co-authored by one of the inventors of the present invention. (Campbell & Jacobs, Detection of Buried Landmines by Compton Backscatter Imaging, Nucl Sci & Engr, 110, 417, 1992). This configuration proved effective in the detection of buried land mines, including all-plastic land mines.
The LMR system disclosed by Campbell & Jacobs comprised an array of detectors which included both collimated detectors and uncollimated detectors. The collimated detectors disclosed are simple rigid shadow shields. The method disclosed is based on the separation of first scatter detection from the multiple scatter detection by image subtraction methods. Thus, the LMR detectors disclosed by Campbell & Jacobs count either essentially single-scatter (uncollimated) or multiple-scatter photons (collimated) which are slightly influenced by the first scatter distribution. There is no structure or methodology disclosed or suggested for obtaining primarily a given (multiple) scatter component or to eliminate a particular (multiple) scatter component.